A power distribution system interconnected to a power distribution transformer station employs a structure spreading dendritically to system terminals from the transformer station, and includes a plurality of consumers, such as houses, business facilities, and factories, that is, loads. Since the power consumption amounts by the consumers change from hour to hour and the number of consumers is large, the voltage of the bus of the power distribution transformer station interconnected to the power distribution system changes. In order to suppress fluctuation of the bus voltage of the power distribution transformer station due to this load change, conventionally, voltage adjusting devices, such as a transformer that can be tap switched, and phase adjusting facilities are provided to said transformer station.
Meanwhile, in recent years, introduction of renewable energy is advancing actively to cope with global environmental issues and to ensure a stable supply by the diversification of energy sources, and the introduction of distributed power supplies, such as solar power generation and wind power generation, to the power system is increasing steadily. These distributed power supplies are mainly interconnected to a power distribution system.